This invention relates to a multiple-articulated robot control apparatus for eliminating robot arm vibration by effecting feedback compensation of disturbance due to interference torque when the robot arm is driven.
An ordinary variable program robot possesses feedback controllers which move the joints of a manipulator from a present value to a designated target value. In accordance with these controllers, the effect which motion along one axis has on other axes is regarded as disturbance in the feedback control system without producing a model of the detailed dynamics of the mutually interfering joints when deciding an actuator signal.
FIG. 3 is a block diagram of a feedback control system. In order to compensate for accumulation of the error due to the abovementioned disturbance on a realtime basis, actual motion is measured, an output from an arm servomotor a serving as a plant is compared with a target response and is subjected to computations by a control rule b having a predetermined feedback gain with respect to the error, and the input to the plant is varied dynamically. However, in a case where a torque signal for the arm required for a robot activity is applied to a multiple-articulated robot as the abovementioned actuator signal, the torques for the respective axes generated as the actual response interfere with one another. The arm vibration thus brought about includes frictional and gravitational forces having non-linear components. In particular, in terms of eliminating path error in a welding operation or the like, it is essential that these be accurately determined.
With regard to arm vibration caused when each arm is feedback-controlled by such a joint driving servomotor, the conventional practice is, say, to compute each axial torque based on a movement command along each axis and correct the torque signal applied to the arm.
The abovementioned feedback control rule requires realtime computation. Though each servomotor provides feedback with regard to a velocity signal in such case, an acceleration signal cannot be obtained unless a position command signal along each axis is differentiated twice. Further, in a conventional control method in which a torque value is computed from this acceleration and velocity, about 16 ms of time is required as the computation period. Accordingly, a problem encountered is that vibration components having high frequencies cannot be removed.